Noise: The 85 Decibel Line and Hearing Conservation

Why this matters

Noise-induced hearing loss is the exposure a tradesperson most reliably takes home, and it gives no signal on the day beyond a ringing that fades by dinner. The loss starts in the high frequencies, around 4,000 Hz, where the consonants that separate "fifteen" from "fifty" live, so the first symptom is a tech who hears fine in a quiet room and cannot follow a conversation in a restaurant. It does not come back. The tools that cause it are on every truck.

There are three different 85-or-90 lines in play, written by three different bodies for different purposes, and a shop that does not know which one binds which job tends to apply none of them. This card is about which line, which tools cross it, and why the stricter yardstick is the better one to manage to. The program obligations under the general-industry standard (monitoring, audiometry, training, records) are owned elsewhere: see related: What Hearing Conservation Actually Requires.

Three yardsticks, three jobs

General industry, 29 CFR 1910.95. An 8-hour time-weighted average (TWA) of 90 dBA is the permissible exposure limit and 85 dBA is the action level that triggers a full hearing conservation program. Both use a 5 dB exchange rate: every 5 dB louder halves the allowed time, so 95 dBA is allowed for 4 hours and 100 dBA for 2. Routine maintenance and service work and a shop's own fabrication bench generally fall here; OSHA draws the line between maintenance and construction (which by definition includes alteration and repair) case by case.

Construction, 29 CFR 1926.52. Table D-2 permits 90 dBA for 8 hours on the same 5 dB exchange rate, but there is no 85 dBA action level in the construction standard. Where exposure exceeds the table, 1926.52(d)(1) requires "a continuing, effective hearing conservation program" without listing what that program must contain, and 1926.101 requires hearing protection where the table is exceeded. Impulse noise is capped at 140 dB peak at 1926.52(e). New construction, alteration and renovation, including much of a remodel, fall here, so the same shop can be under 1910 on Monday's repair and 1926 on Tuesday's addition.

NIOSH recommended exposure limit (REL). 85 dBA as an 8-hour TWA with a 3 dB exchange rate: every 3 dB halves the allowed time, so 88 dBA is allowed for 4 hours, 91 for 2, 94 for 1, and 100 dBA for about 15 minutes. NIOSH is a research agency, so the REL binds nobody by itself; it is a recommendation that some employers adopt by policy. NIOSH's 1998 criteria document estimated that even at 85 dBA over a 40-year working life, roughly 8 percent of workers develop material hearing impairment beyond what age alone causes, which is the reason not to treat 90 as safe.

Why the exchange rate is the real difference. Sound energy doubles every 3 dB, so the 3 dB rate is the equal-energy rule: twice the energy, half the time. OSHA's 5 dB rate, set decades ago, assumes the ears recover during quiet breaks in intermittent exposure. Field trades are exactly the intermittent pattern the 5 dB rate credits, so short, loud bursts on a service call count for far less under OSHA than under NIOSH. That gap is widest for the very tools trades use most: under OSHA, 15 minutes at 100 dBA is 12.5 percent of a day's allowance; under NIOSH it is the whole day's allowance.

Tools that cross the line

Ranges below are typical at the operator's ear, as reported across NIOSH and manufacturer measurements. They vary with blade, material, enclosure and distance, which is why the card measuring your own jobs exists. See related: How to Measure Noise on Your Own Jobs.

Two rules of thumb travel well. If you have to raise your voice to be heard by someone an arm's length away, the level is probably 85 dBA or more. And every 3 dB is double the energy: a grinder at 104 dBA delivers twice the noise dose per minute of one at 101, even though the numbers look close.

Impulse noise is its own category. A powder-actuated tool or a framing nailer fired indoors produces a peak that a time-weighted average flattens into almost nothing, while the single pressure spike can damage the inner ear directly. Treat any tool that fires as requiring protection on every shot, regardless of what the day's average says.

Some chemicals add to the damage. Solvents such as toluene and xylene, lead and carbon monoxide are ototoxic, meaning they harm hearing on their own and appear to worsen noise damage. A tech grinding a lead-painted surface in a closed room with a gas tool running is stacking three of them.

One day, three yardsticks

An electrician's day: 1.5 hours drilling anchors into concrete with a rotary hammer at 102 dBA, 0.5 hours on an angle grinder at 98 dBA, and 6 hours of terminations and travel at 78 dBA. The levels are illustrative, the kind a sound level meter at the ear would plausibly read. The OSHA dose method is the one the general-industry card derives; NIOSH uses the same shape with an 85 criterion and a 3 dB rate.

Segment         OSHA          NIOSH
                allow  dose   allow  dose
102 dBA, 1.5 h  1.52h  0.99   0.16h  9.52
 98 dBA, 0.5 h  2.64h  0.19   0.40h  1.26
 78 dBA, 6.0 h  none   0.00   40.3h  0.15
                (under 80)
Total dose             1.18          10.93
OSHA TWA  = 16.61 x log10(1.18) + 90 = 91.2 dBA
NIOSH TWA = 10 x log10(10.93) + 85   = 95.4 dBA

Under 1910.95, 91.2 dBA is above the 90 dBA PEL: a hearing conservation program is owed, feasible controls are owed, and protectors must be worn. Under 1926.52, the same day exceeds Table D-2, so the continuing, effective program and protectors are owed. Under the NIOSH REL, the dose is 10.93, nearly eleven times the recommended daily dose; the electrician exceeded it inside the first 10 minutes of drilling.

Shorten the drilling to 1 hour and the answers split. The OSHA dose becomes 0.66 plus 0.19, or 0.85, a TWA of 88.8 dBA. Under 1910.95 that is below the PEL but above the 85 action level, so the program is still owed and protectors must be made available. Under 1926.52, 88.8 is inside Table D-2 and the table triggers nothing. Under NIOSH the dose is 6.35 plus 1.26 plus 0.15, or 7.76, a TWA of 93.9 dBA, still nearly eight times the recommendation. Thirty minutes less drilling moved this tech out of a construction obligation without moving the ear's risk much at all.

Note what the 78 dBA segment does. Under OSHA, levels below 80 dBA contribute nothing. Under NIOSH, six hours at 78 still used 15 percent of a full day's allowance, which is why a tech in a loud mechanical room all day can exceed the REL without touching a power tool.

Managing to the stricter line

The practical recommendation is to manage the shop to the NIOSH REL even where the law asks for less, because the cost of doing so is mostly protectors and habits, and the cost of not doing so is permanent.

• Engineering first, as the hierarchy orders it. A shrouded grinder with a dust extractor is often quieter at the ear than a bare one; a sharp blade cuts quieter than a dull one; a battery blower or saw is commonly several dB quieter than its gas counterpart. See related: The Hierarchy of Controls on a Service Call.
• Distance is a control. In open air, level falls about 6 dB each time distance from a point source doubles, so the helper standing 6 feet from a cut-off saw instead of 3 receives roughly a quarter of the energy. Indoors, reflections from hard walls erode most of that.
• Protection for the tools in the table, every time. For the loudest group, plugs and muffs together. See related: How to Fit Earplugs So They Actually Work.
• Baseline audiograms even where no rule requires them. A construction-only shop has no audiometric requirement spelled out, but a baseline at hire is the only way to show later whether a loss happened on your watch.

Where these lines mislead

A TWA is about the person, not the tool. The same grinder puts one tech over and another under, depending on minutes. Labeling a tool "over 85" tells you it can contribute; only the day's mix tells you whether a person crossed.

Under the PEL is not under the damage. The 90 dBA PEL is a legal floor set by a 5 dB method. Hearing loss accumulates below it, and the NIOSH estimate of excess risk at 85 dBA is not zero.

Which Part applies is a fact about the work, not the shop. A shop that does both service and renovation needs to know which hat the crew wore that day before it can say which table its exposure is read against.

References

• 29 CFR 1910.95, Occupational Noise Exposure (general industry), Table G-16 and the 85 dBA action level
• 29 CFR 1926.52, Occupational Noise Exposure (construction), Table D-2, (d)(1) program and (e) impulse limit; 29 CFR 1926.101, Hearing Protection
• NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure (1998), the 85 dBA REL with a 3 dB exchange rate
• See related: What Hearing Conservation Actually Requires; How to Measure Noise on Your Own Jobs; How to Fit Earplugs So They Actually Work; Dose, Route, and the Exposure You Cannot See